Image sensors include a substrate having a plurality of pixels. Each pixel typically includes a photosensitive area that converts incident light into charge packets. One of more transistors are connected to the photosensitive area for various purposes, such as passing the charge therefrom and for signal processing of the charge packet that may be external to the imaging area. Each of the transistors is connected to a voltage source for permitting the transistors to be operated as desired. A plurality of buses connects the transistors to voltage sources.
The buses are typically layered, one above another, and they are connected together through electrical connection, VIAs and pre-contacts, and they eventually pass through an internal seal ring to an external pad. These external pads on the wafer DIEs are eventually connected to package leads to form the electrical connections.
Typically the buses are made of either aluminum (Al) or copper (Cu). However, extending the copper outside the internal seal ring exposes the copper to air and the like which causes the copper to be oxidized. Aluminum is less likely to be oxidized when exposed to air; however, its conductivity is lower than copper.
Consequently, a need exists for image sensors that use copper for its conductive properties, but also resists its tendency to be oxidized when exposed to air.